1. Field of the Invention
The present invention relates to a photoelectric conversion apparatus and an image pickup system using the photoelectric conversion apparatus.
2. Description of the Related Art
As photoelectric conversion apparatuses used for digital cameras, video cameras, or the like, charge-coupled device (CCD) photoelectric conversion apparatuses or metal-oxide semiconductor (MOS) photoelectric conversion apparatuses have been available. In particular, in recent years, the technological development of complementary metal-oxide semiconductor (CMOS) photoelectric conversion apparatuses has been actively conducted due to advantages of a reduced power consumption and an excellent compatibility with semiconductor processes. Furthermore, in order to satisfy a requirement for increasing the number of pixels and to improve the sensitivity per unit pixel, various configurations in which the number of MOS transistors per unit pixel is reduced have been suggested.
Under such circumstances, in order to increase the light-receiving area of a photoelectric conversion element, a configuration in which the number of MOS transistors is reduced has been examined. For example, a photoelectric conversion apparatus that selects pixels in units of rows by controlling the drain potentials of reset MOS transistors is disclosed, for example, in Japanese Patent Laid-Open No. 11-355668. In addition, a photoelectric conversion apparatus that selects pixels in units of rows by controlling, by a pixel power supply driving circuit, the drain voltages of reset transistors and amplifying transistors that are commonly connected is disclosed, for example, in Japanese Patent Laid-Open No. 2005-005911.
In a case where a further increase in the number of pixels, finer wiring, and the like are required, when the configuration described in Japanese Patent Laid-Open No. 11-355668 or 2005-005911 is used, the load on a power supply line for supplying a voltage to a pixel power supply voltage circuit or to a reset MOS transistor is increased in accordance with an increase in the size of a photoelectric conversion area.
Thus, the time necessary for charging and discharging the power supply line is increased. As a result, a problem may occur in that the time necessary for reading a signal is increased and the frame rate is thus reduced. In addition, due to a voltage drop, a power supply voltage supplied to the drain of a reset MOS transistor is varied in a photoelectric conversion area. In accordance with an increase in the size of the photoelectric conversion area, the variation increases. Thus, a phenomenon called shading may often occur in which a difference in signal output levels is generated within the photoelectric conversion area.